ELECTRICITY. 



427 



ICxperi- 

 icnts of 

 Saussure. 



Born 

 Bicd 



History, gativc and positive electricity. In these experiments . 



'""V"*' the bodies which were evaporated were insulated, and 

 when the indications of electricity appeared to be in- 

 stantaneous, it was communicated, by a chain or wire, 

 to a small electrometer like that of Cavallo's ; but when 

 it was supposed that the electricity increased by degrees, 

 they employed the instrument invented by Volta for 

 condensing small quantities of the fluid. Having placed 

 iron filings in a VPSSC! with a large aperture, they poured 

 upon the filings sulphuric acid, diluted with three parts 

 of water. A brisk effervescence took place ; inflam- 

 mable air was rapidly disengaged, and at the end of 

 some minutes the condenser was so charged with elec- 

 tricity, that it produced a strong spark. The electri- 

 city was in this case negative. When fixed air and 

 nitrous gas were produced, by pouring sulphuric acid 

 and nitrous acid upon powdered chalk; and when char- 

 coal was burned upon an insulated chafing dish, similar 

 results were obtained. There seems, however, to have 

 been some uncertainty in some of the other e.xperi- 

 ments ; for when water was poured upon insulated and 

 heated stoves of hammered iron, the electricity was ne- 

 gative in the first experiment, and positive in two other 

 experiments. See p. 4fc. 



M. J)e Saussure made a series of experiments of a 

 similar kind. He found that the evaporation of water, 

 by simple ebullition, produced negative electricity, but 

 was surprised to find, that when he plunged red hot 

 iron in a small quantity of water, at the bottom of a 

 metallic vessel, it produced positive electricity. In 

 order to discover the cause of this variation, he em- 

 ployed vessels of iron, copper, and silver, &c. strong- 

 ly heated, and into these he poured a certain quantity 

 of the fluid which he wished to convert into vapour. 

 The-e fluids were distilled water, spirit of wine, and 

 ether, and he marked the duration of the evaporation, 

 the nature and degree of the electricity, as well as the 

 state of the vessel and of the vapours that were pro- 

 duced. In ;, no electricity whatever appeared, 

 in others the electricity was positive, and in others ne- 

 gative. M. De Saussure was of opinion, that when the 

 water w;-.s decomposed during its conversion into va- 

 pour, or the body which was in contact with ft, a new 

 quantity of electric matter is evolved, and the vessel 

 which is employed in the experiment receives a positive 

 or a negative electricity, or no electricity at all, ac- 

 cording as the quantity of fluid generated is greater, 

 less, or equal to that which the evaporation carries off 

 from the \r-M-l. M. de Saunsurr has also made some 

 intere-tiiig observations on the electricity of the atmo- 

 sphere. See pages 46'3 and 4S 1 . 



Our countryman, Dr John Robison, late professor of 

 natural philosophy in the university of Edinburgh, 

 made a number of ingenious experiments on electri- 

 city. So early as the year 1 "(>:), Dr Robison had m.vlc 

 numerous attempts to determine the law of electric ac- 

 tion. By means of a very admirable electrometer, of 

 his own invention, with which he could measure the 

 attractions of oppositely electrified bodies, he got ab- 

 solute measures of the attractive forces. He obtained 

 more than a hundred results with different intru- 

 ments of different si/es ; and not one of these n 

 deviated from the medium |th of the whole force, and 

 there were very few that deviated V^th. He mea- 

 sured nil the forces by a linear scale, and expressed 

 them by ordinates to a base, on which the distances 

 were set off from a fixed point. A regular curve was 

 then drawn through the summits of the ordinates, 

 and he was thus enabled to observe, in the distinctcst 

 manner, the coincidence or the deviation of his expcri- 



History. 



B\ peri- 

 menu of 

 Or Uobi- 



1740. 



1SH5. 



ments. The general result of these experiments was, 

 that the mutual repulsion of two spheres, electrified ci- 

 ther positively or negatively, varied in oa , or was 



nearly as the inverse ratio of the square of the distance. 

 When the experiment was made on the attractive force 

 of balls oppositely electrified, the irregularities were 

 greater than in the preceding case, amounting, in some 

 instances, to fth of the whole force. The results, how- 

 ever, deviated rather less than the former, from the in- 

 verse duplicate, ratio of the distances; but the devia- 

 tion was in defect, as the other was in excess. From 

 these results, Dr Robison concluded, that the action 

 between two spheres was like that of gravity, in the 

 inverse ratio of the squares of the distances" of their 

 centres. It is much to be regretted, that Dr Robison 

 did not publish some account of these conclusions at the , 



time when he obtained them. He would then have 

 been entitled to a considerable share of that honour 

 which has been bestowed on Coulomb. See page 4K). 



Towards the end of the IJth century, electricity was 

 assiduously cultivated by a great number of eminent 

 individuals, who extended the boundaries of the science 

 by numerous experiments, and by the invention of in- 

 genious and useful instruments. 



By the aid of an admirable electrifying machine, and Van 

 powerful batteries, M. Van Marum performed a series Msrum -' 

 of interesting experiments on the fusion and the oxida- 

 tion of metals by the electric shock. He obtained some 

 curious results respecting the magnetical effects of elec- 

 tricity ; and he made numerous experiments to ascer- 

 tain the influence of the electric fluid upon animal and 

 vegetable bodies. 



The late Mr Cavallo made many important additions Cavallo. 

 to the science. His experiments with electrical kites, 

 and thunder rods, added greatly to our knowledge of 

 atmospherical electricity ; and his instruments for mea- 

 suring, doubling, condensing, and multiplying elec- 

 tricity, bespeak a mind full of ingenuity, and intimate- 

 ly acquainted with the science which he cultivated. 



Mr Nicholson made several curious experiments on Nicholson. 

 the form of the electric spark, and on the excitation of 

 electrical machines ; and he enriched the science with 

 two elegant instruments, which he called the spinning 

 condenser, and the revolving doubler. 



Electricity has derived new light from the labours of Hur. 

 that vencr.V>Ie philosopher M. Hauy, who h:is discover- 

 ed, that the property of becoming electrical by heat, 

 resides in mesotype, boracite, calamine, and prehnite, as 

 well as in the tourmaline and the topaz. He found, 

 that the boracite possessed eight electrical poles ; and 

 we owe to him the fine discovery, that the polurity 

 which these minerals acquire from heat, is related to 

 the secondary form of their crystals, those which have 

 this property, deviating from that symmetry of form 

 which is conspicuous in other minerals. 



Mr Cuthbertson had the great merit of giiing a new cmhbert- 

 degrce of elegance and power to the electrical appara-son. 

 tus. His improvements on the plate glass machine ; 

 his mode of constructing and improving batteries ; his 

 new condenser, and his compound electrometer ; entitle 

 him to be considered as one of the most ingenious prac- 

 tical electricians of the present day. Along with Van 

 Troostwyk, he was the first that decomposed water by 

 the electric shock ; and he made many interesting ex- 

 periments on the fusion and oxidation of metals by elec- 

 tricity. 



Mr Brooke was the first person who proposed the Brooke, 

 balance electrometer, and from numerous experiments 



